1. Field of the Invention
The present invention relates to new types of CO2 refrigerant compressor-use bearings improved in wear resistance, a compressor that employs these bearings, and such an air conditioner, refrigerator, and hot-water supply machine that each employs the bearings.
2. Description of the Prior Art
Cast iron, bronze-based materials, aluminum-alloying materials, or other metallic materials, or resin-containing materials, or composite materials consisting of resin and a metal, have been employed as bearing materials for conventional refrigerant compressors. Bronze-based materials have contained a great quantity of lead. Numerous types of sliding materials laden with lead have also been most commonly used in other machines. Under these circumstances, the shafts inserted into bearings have been provided with surface treatment to prevent galling. When a bearing material other than cast iron was to be used, the occurrence of galling and unusual wear has been prevented by adopting a material dissimilar to the shaft material.
The bearing materials formed by impregnating graphite-containing carbon materials with aluminum are disclosed in Japanese Application Patent Laid-Open Publication No. Hei 02-248676 and Hei 02-275114.
In conventional compressors, increases in bearing load due to the improvement of performance have led to partial breakage of the lubricating film formed by an oil, and this event has been inciting a so-called “boundary lubrication” status under which local direct contact occurs between the bearing and the shaft. Boundary lubrication is also incited by the operational start of the compressor or the excessive ingress of the refrigerant. Under such boundary lubrication status, conventional metal-based bearings, resin-based bearings, surface-treated shafts, and the like have been prone to suffer galling or thermal seizure. Although bearing loads can be reduced by increasing the inside diameters of the bearings or increasing the length of the bearing section, these methods have had their limits since the space required for the bearings is limited in motor-containing compressors of the enclosed type.
It is known that the lead bronze and antimony alloys in which the lead or antimony having a lubricating property is contained as one of the respective components, composite materials consisting of lead or antimony and carbon, and other materials do not easily cause thermal seizure or galling. At the same time, however, there is also the fear that lead and antimony affect environments and the human body. These elements also fall under the category of the substances whose use is regulated by the pollutants release and transfer registration (PRTR) law. For lead bronze, antimony alloys, and composite materials consisting of lead or antimony and carbon, although the improvement of the respective anti-wear characteristics under an oil-free status or severe conditions is accomplished by utilizing the property that the melting point of each such metal is low. Even so, significant wear occurs to the parts used at high temperature or put into continued use under a severe sliding status.
No such conventional bearings made of carbon materials impregnated with aluminum are disclosed that employ a metal other than aluminum or that a graphite content or the porosity rate obtained after impregnation has been provided is shown.